Using an HTML button to call a JavaScript function


I am trying to use an HTML button to call a JavaScript function.

Here's the code:

<input type="button" value="Capacity Chart" onclick="CapacityChart();">

It doesn't seem to work correctly though. Is there a better way to do this?

Here is the link: click on the capacity tab in the bottom left section. The button should generate an alert if the values are not changed and should produce a chart if you enter values.

7/23/2017 11:44:34 AM

Accepted Answer

There are a few ways to handle events with HTML/DOM. There's no real right or wrong way but different ways are useful in different situations.

1: There's defining it in the HTML:

<input id="clickMe" type="button" value="clickme" onclick="doFunction();" />

2: There's adding it to the DOM property for the event in Javascript:

//- Using a function pointer:
document.getElementById("clickMe").onclick = doFunction;

//- Using an anonymous function:
document.getElementById("clickMe").onclick = function () { alert('hello!'); };

3: And there's attaching a function to the event handler using Javascript:

var el = document.getElementById("clickMe");
if (el.addEventListener)
    el.addEventListener("click", doFunction, false);
else if (el.attachEvent)
    el.attachEvent('onclick', doFunction);

Both the second and third methods allow for inline/anonymous functions and both must be declared after the element has been parsed from the document. The first method isn't valid XHTML because the onclick attribute isn't in the XHTML specification.

The 1st and 2nd methods are mutually exclusive, meaning using one (the 2nd) will override the other (the 1st). The 3rd method will allow you to attach as many functions as you like to the same event handler, even if the 1st or 2nd method has been used too.

Most likely, the problem lies somewhere in your CapacityChart() function. After visiting your link and running your script, the CapacityChart() function runs and the two popups are opened (one is closed as per the script). Where you have the following line:


Try the following instead:"text/html");

When I saw your code I thought you were writing it specifically for IE. As others have mentioned you will need to replace references to document.all with document.getElementById. However, you will still have the task of fixing the script after this so I would recommend getting it working in at least IE first as any mistakes you make changing the code to work cross browser could cause even more confusion. Once it's working in IE it will be easier to tell if it's working in other browsers whilst you're updating the code.

2/14/2017 10:24:59 PM

I would say it would be better to add the javascript in an un-obtrusive manner...

if using jQuery you could do something like:


<input type="button" value="Capacity Chart" id="MyButton" >

Your HTML and the way you call the function from the button look correct.

The problem appears to be in the CapacityCount function. I'm getting this error in my console on Firefox 3.5: "document.all is undefined" on line 759 of bendelcorp.js.


Looks like document.all is an IE-only thing and is a nonstandard way of accessing the DOM. If you use document.getElementById(), it should probably work. Example: document.getElementById("RUnits").value instead of document.all.Capacity.RUnits.value


This looks correct. I guess you defined your function either with a different name or in a context which isn't visible to the button. Please add some code


Just so you know, the semicolon(;) is not supposed to be there in the button when you call the function.

So it should just look like this: onclick="CapacityChart()"

then it all should work :)


One major problem you have is that you're using browser sniffing for no good reason:

if(navigator.appName == 'Netscape')
      vesdiameter  = document.forms['Volume'].elements['VesDiameter'].value;
      // more stuff snipped
      vesdiameter  = eval(document.all.Volume.VesDiameter.value);
      // more stuff snipped

I'm on Chrome, so navigator.appName won't be Netscape. Does Chrome support document.all? Maybe, but then again maybe not. And what about other browsers?

The version of the code on the Netscape branch should work on any browser right the way back to Netscape Navigator 2 from 1996, so you should probably just stick with that... except that it won't work (or isn't guaranteed to work) because you haven't specified a name attribute on the input elements, so they won't be added to the form's elements array as named elements:

<input type="text" id="VesDiameter" value="0" size="10" onKeyUp="CalcVolume();">

Either give them a name and use the elements array, or (better) use

var vesdiameter = document.getElementById("VesDiameter").value;

which will work on all modern browsers - no branching necessary. Just to be on the safe side, replace that sniffing for a browser version greater than or equal to 4 with a check for getElementById support:

if (document.getElementById) { // NB: no brackets; we're testing for existence of the method, not executing it
    // do stuff...

You probably want to validate your input as well; something like

var vesdiameter = parseFloat(document.getElementById("VesDiameter").value);
if (isNaN(vesdiameter)) {
    alert("Diameter should be numeric");

would help.


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